Substrate effect of STM-induced luminescence from porphyrin molecules

We investigated scanning tunneling microscope (STM)-induced luminescence from Meso-tetrakis (3,5-di-tertiarybutyl-phenyl) porphyrin (H2TBPP) thin films on various metal substrates (copper, platinum and silver) under ambient conditions. Molecular fluorescence similar to the corresponding photoluminescence was observed from the H2TBPP/Ag and H2TBPP/Pt, but not H2TBPP/Cu, depending on the spectra of the surface plasmons of the substrates. The results support the mechanism that intense molecular fluorescence from porphyrin film on the noble metals is a result of enhancement of molecular excitation by substrate surface plasmons.